Exclusive electroproduction of K+ Lambda and K+ Sigma^0 final states at Q^2 = 0.030-0.055 (GeV/c)^2

Cross section measurements of the exclusive p(e,e'K+)Lambda,Sigma^0 electroproduction reactions have been performed at the Mainz Microtron MAMI in the A1 spectrometer facility using for the first time the Kaos spectrometer for kaon detection. These processes were studied in a kinematical region not covered by any previous experiment. The nucleon was probed in its third resonance region with virtual photons of low four-momenta, Q^2= 0.030-0.055 (GeV/c)^2. The MAMI data indicate a smooth transition in Q^2 from photoproduction to electroproduction cross sections. Comparison with predictions of effective Lagrangian models based on the isobar approach reveal that strong longitudinal couplings of the virtual photon to the N* resonances can be excluded from these models.Comment: 16 pages, 7 figure

The influence of decision-making in tree ring-based climate reconstructions.

Tree-ring chronologies underpin the majority of annually-resolved reconstructions of Common Era climate. However, they are derived using different datasets and techniques, the ramifications of which have hitherto been little explored. Here, we report the results of a double-blind experiment that yielded 15 Northern Hemisphere summer temperature reconstructions from a common network of regional tree-ring width datasets. Taken together as an ensemble, the Common Era reconstruction mean correlates with instrumental temperatures from 1794-2016 CE at 0.79 (p < 0.001), reveals summer cooling in the years following large volcanic eruptions, and exhibits strong warming since the 1980s. Differing in their mean, variance, amplitude, sensitivity, and persistence, the ensemble members demonstrate the influence of subjectivity in the reconstruction process. We therefore recommend the routine use of ensemble reconstruction approaches to provide a more consensual picture of past climate variability

Strange hadrons – strangeness in strongly interacting particles

In 2007 the Mainz Microtron MAMI has been upgraded to 1.5 GeV electron beam energy, crossing the energy threshold for open strangeness production. The strangeness quantum number, as carried by the strange quark, provides valuable information on the contribution of individual quark flavours to hadronic processes. Theoretically, the strange quark with its rest energy of order 150 MeV is particularly interesting because it can neither be treated as a massless nor as a heavy quark. Experimentally, an instrument of central importance for the charged kaon electro-production off the proton or light nuclei at MAMI is the magnetic spectrometer Kaos that was installed recently and is now routinely operated by the A1 collaboration

First measurements of Lambda and Sigma0 hyperons in elementary electroproduction at MAMI

International audienc

Towards a reconstruction of Blue Nile baseflow from Ethiopian tree rings

Most of the water in the River Nile originates from monsoonal rainfall over the Ethiopian Highlands. Despite warnings of future climate change, little is known about the historical variability in this supply, particularly at annual resolution. Development of tree-ring records in this region has been limited by the occurrence of bi- or multimodal rainfall regimes, causing the development of multiple growth rings that cannot be dated with confidence. In this study, we identified annual rings in 30 Juniperus procera trees from northwest Ethiopia by dendrochronology and AMS radiocarbon dating. Carbon isotope ratios(4 series) and ring widths (73 series) were measured. The carbon isotope series did not contain strong trends possibly attributable to increased anthropogenic atmospheric CO2 concentrations or the juvenile effect. Both carbon isotope values and ring widths were strongly correlated with Blue Nile baseflow, and from composite chronology indices (r=0.75, p <0.01), a preliminary reconstruction of Blue Nile baseflow back to AD 1836 was developed. Subsample signal strength remained above 0.85 for most of the reconstruction. Uncertainty bands were relatively narrow and the reliability of the preliminary reconstruction was confirmed by correspondence with reported years of drought and famine. The preliminary reconstruction is characterized by an exceptional decline in baseflow during the late AD 1960s. Flows recovered during the late 1990s. Additional sampling is advised to increase replication, spatial coverage and length of the preliminary reconstructio